Crohn’s disease as an immunodeficiency

Abstract

The pathogenesis of Crohn's disease (CD) has widely been regarded as the consequence of a dysregulated T-cell-mediated response to intestinal microbes, and the majority of the worldwide research effort has focused on characterizing and treating the chronic inflammatory phase of the disease. However, recent molecular biological and clinical investigations indicate that CD is actually a primary immunodeficiency. At first counter-intuitive, the apparent paradox of a pathogenic innate immune defect can be linked mechanistically to the granulomatous chronic inflammation characteristic of the disease. Genome-wide association studies have corroborated the involvement of innate immune dysfunction in the pathogenesis of CD, but less than 20% of the heritable risk is accounted for. By contrast, in vitro and in vivo stimulation of the immune system has highlighted novel areas of interest that may lead to the development of targeted therapeutic and diagnostic tools. Keywordsbacteria; Crohn's disease; immunodeficiency; innate immunity; macrophage; neutrophil Established intestinal lesions in Crohn's disease (CD) contain a massive, mixed inflammatory cell infiltrate associated with a complex storm of cytokines in a selfperpetuating, chronic inflammatory response [1][2][3]. Most research to date has focused on the the immunological characteristics of established lesions and drawn inferences about their initiation. The predominance of a classically Th1-associated cytokine profile in these lesions led to the assumption that T lymphocytes were central to the initial pathogenesis. More recently, the role of regulatory (Treg) FoxP3 + and IL-23-induced responsive Th17-type T lymphocytes has gained popularity [2,4,5]. Treg cell populations are diminished in patients with CD [6] and, although the hypothesis of CD as an immunodeficiency does not necessarily exclude defects in T-cell function, to date, no convincing intrinsic (primary) defect has been identified to implicate these cells in the pathogenesis of human CD.The hypothesis that immunodeficiency underpins the development of CD seems, at first, to be in direct contrast with histological observations of established intestinal lesions and the † Author for correspondence: Tel.: +44 207 679 6170 Fax: +44 207 679 0967 b.hayee@nhs.net. Financial & competing interests disclosure The authors have no other relevant affiliations or financial involvement with any organization or entity with a financial interest in or financial conflict with the subject matter or materials discussed in the manuscript apart from those disclosed. Europe PMC Funders Group Association between immunodeficiency diseases & CDThere is a well-known and strong association between primary immunodeficiency disorders and non-infectious granulomatous intestinal inflammation. Chronic granulomatous disease (CGD), glycogen storage disease type 1b, leukocyte adhesion deficiency, Chediak-Higashi and Hermansky-Pudlak syndromes are all strongly associated with intestinal inflammation that is indistinguishable from CD [...

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